JPS6225619B2 - - Google Patents

Description

Detailed Description of the Invention The present invention involves polishing a glass product in a polishing bath containing sulfuric acid and hydrofluoric acid, and polishing the final polished product with sulfuric acid and/or water. It concerns a method of cleaning.

It is already known to polish glass products (pressed glass and frosted glass products) by chemical methods using polishing baths containing sulfuric acid and hydrofluoric acid. In this method, due to the reaction with the glass components of the surface of the product that occurs during acid polishing, a firm adherent layer of reaction products is formed on the surface. Generally, the products of this reaction are sulfates, fluorides, and furosilicates with the cations contained in the glass. This layer of reaction product prevents the polishing process, ie the action of the polishing acid on the glass surface, until the reaction has completely stopped. In the past, it has always been necessary to remove the layer formed by the reaction products of the polishing process so that the polishing process can be continued. For this reason, the polishing process was interrupted and the film formed by the reaction product was washed away, and this operation was repeated many times until the desired degree of polishing was achieved. Furthermore, in the past, water was used to wash away the deposited layer from polishing, but this method had a major drawback because the polishing treatment and cleaning were performed alternately, and a large amount of water was introduced into the polishing bath and diluted. I had it. On the other hand, it produces an acidic wash which not only consumes acid unduly, but also has to be neutralized in a meticulous manner before being discharged into the river, which is a serious problem. occurred.

German Patent No. 2949383 discloses that dissolved sodium and/or calcium ions are removed from the polishing acid continuously or batchwise or discontinuously, thereby improving polishing in a single immersion. In other words, the process of alternating the polishing bath and cleaning bath (hereinafter referred to as "alternating treatment") can be reduced to a few times, or the desired finish can be achieved in one polishing and cleaning process. It is stated that it will be done. In this prior art, sodium and/or calcium ions are removed from the polishing bath by adding fluorosilicic acid to precipitate the corresponding fluorosilicate, and then removing the fluorosilicate by, for example, filtration or centrifugation. It was then removed from the polishing bath. In addition to fluorosilicic acid, phosphoric acid and/or acetic acid and optionally malonic, oxalic or tartaric acid were introduced into the polishing bath to promote precipitation. In the prior art, other possibilities for removing alkali ions from polishing baths include electrolysis using mercury cells or cells with cationic semipermeable membranes. In this method, alkaline ions are extracted from a polishing bath.
There is also the possibility of using cation exchangers to remove alkali ions from the polishing bath.

Furthermore, in the method described in the earlier German publication no. was added to maintain the degree of dissociation of hydrofluoric acid as high as possible. In a polishing bath prepared from hydrofluoric acid, sulfuric acid (30% concentration), water and a small amount of oleum of unknown concentration, approx.
The addition of 0.7 g/P ₂ O ₅ as a "control agent" has been known since 1930 from US Pat. No. 1,777,321.

In addition, West German Patent No. 1189681 specifies 55
A polishing bath with a concentration of ~67% sulfuric acid and a concentration of 5-7% hydrofluoric acid is used at a temperature of 55-70°C, and the bath is also supplemented with heavy metal salts or potassium permanganate with strong oxidizing power or It is described that the state of the salt deposit layer formed on the glass surface can be influenced by adding chromium oxide.

In addition to requiring the glassware to be polished to be subjected to several alternating treatments with polishing and cleaning baths, the consumption of hydrofluoric acid and sulfuric acid also makes it an economical method for polishing glassware. However, this is extremely important. The consumption of acids, especially of hydrofluoric acid, depends on the composition of the polishing bath, and such consumption will affect the polishing time per batch of glassware or whether the polishing bath should be renewed. Or, if there is no playback, it affects the number of batches to be polished. Due to the density of the highly concentrated salts precipitated on the glass surface, the polishing rate of the polishing bath, which is essential for the polishing process, is inversely proportional to the concentration of sulfate and fluoride ions in the bath. .

The object of the present invention is to polish glass products at a high polishing rate, that is, in a relatively short polishing time, in a polishing bath containing sulfuric acid and hydrofluoric acid, and to polish the finished product using sulfuric acid and hydrofluoric acid. The object of the present invention is to provide a method for submerged cleaning using water and, on the other hand, extending the usability of the polishing bath. Another object of the invention is that the polishing bath can be used without special cleaning means or in an 8-hour exchange regime without having to be renewed at least in part during that time, and at the same time improves the efficiency of the polishing bath. and to improve such polishing baths so that the polishing amount meets all requirements.

In the present invention, the first object is to add to the polishing bath one or more acids that do not have strong oxidizing power but are stronger than hydrofluoric acid and optionally stronger than the second dissociation stage of sulfuric acid. This is achieved by suppressing the dissociation of hydrofluoric acid and sulfuric acid, thereby maintaining a low concentration of fluoride and optionally sulfate ions in the polishing bath. Particularly when polishing rough-cut glass products, it is essential to keep the concentration of fluoride ions as low as possible. In order to polish this type of glassware to the desired degree of polish in a single immersion, the concentration of fluoride ions must be kept particularly low.
The adhesion layer formed during the polishing reaction must be generated on the surface of the glass product in a fine form and with a low adhesion ability so that the adhesion layer is not firmly adhered.

The acids used for the addition of such acids in the present invention are stronger than hydrofluoric acid and preferably also have a higher dissociation constant than the second dissociation stage of sulfuric acid; Strictly speaking, this is different from the addition of fluorosilicic acid for the precipitation of sodium fluorosilicate and/or calcium fluorosilicate in the specification.
The aim of this West German patent is to remove alkali ions from the polishing bath by adding acid, but in the present invention, the dissociation of hydrofluoric acid and sulfuric acid contained in the polishing bath is achieved by adding _a low SO ^2-4 concentration,
In particular, the objective is to suppress the polishing time to a correspondingly short polishing time or the minimum number of alternating treatments between the polishing bath and the cleaning bath, as the polishing rate is necessarily high due to the F ^- concentration.

Provided that the acid to be added satisfies the above conditions, that is, it is a stronger acid than hydrofluoric acid,
Acids suitable for the purpose of the invention include phosphoric acid, monocarboxylic acids such as acetic acid, carboxylic acids such as oxalic acid, malonic acid or phthalic acid, oxycarboxylic acids such as tartaric acid or citric acid. Hydrofluoric acid is not suitable in this case. The reason for this is that new products are continuously generated in the bath and (SiF ₄
This is because the concentration of hydrofluoric acid cannot be adjusted under typical processing conditions because it evaporates in a temperature-dependent manner (as (as)). Acids with strong oxidizing power, such as chromium, are not suitable because of this strong oxidizing effect.

Until now, the dissociation of hydrogen fluoride, and thus the concentration of fluoride ions in the polishing bath, could only be controlled by the concentration of sulfuric acid and the temperature of the bath. A disadvantage of such a method is that the concentration of sulfate ions must be in a constant proportional relationship to the concentration of fluoride ions if satisfactory polishing results are to be obtained. Conventionally, when polishing soda glass for diamond polishing, it was necessary to polish it with sulfuric acid at the highest possible concentration. Therefore, such rough-cut glass was polished using a uniform program with many alternating batch treatments. The dissociation of hydrofluoric acid, ie, the concentration of fluoride in the polishing bath, was reduced only when attempting to increase the concentration of fluoride in the polishing bath.

For the first time in the process of the present invention, which involves adding an acid stronger than hydrofluoric acid to the polishing bath, the fluoride ion concentration, independent of the sulfuric acid concentration, is such that the salts formed during the polishing reaction It was possible to reduce the composition to such a value that it had the ability to adhere to the surface of glass products. The composition, condition, and ability of the salt to adhere to the surface of the glass product are such that the polishing process can be carried out unhindered for a long period of time, and in particular, the desired degree of polishing can be achieved by polishing the glass product according to the present invention. Refers to the composition, condition, and ability to adhere to the surface of glassware as achieved by a single immersion in a rising bath.

Another advantage of the method of the invention is that the polishing method is generally independent of the cationic content (alkali metals, alkaline earth metals) of the glass. The reason for this is that such cationic components influence the dissociation of hydrofluoric acid and thus the concentration of fluoride ions in the polishing bath, and are independent of the concentration of sulfuric acid. If the glass to be treated contains calcium, oxalic acid is not added to the polishing bath. The reason for this is that calcium oxalate is insoluble and precipitates. However, a variety of other useful acids can be used in the process of the invention as described above. Like oxalic acid, tartaric acid can form poorly soluble potassium tartrate if the glass contains potassium and should be avoided.

As mentioned above, a prerequisite for the application of acids in the process of the invention is that such acids are stronger than hydrofluoric acid;
That is, it has a higher dissociation constant than hydrofluoric acid. It is also advantageous for such an acid to have a dissociation constant that is at least between the first and second dissociation stages of sulfuric acid. Note that this applies to most of the acids mentioned above. However, oxalic acid is the second type of sulfuric acid.
Oxalic acid can also reduce the concentration of sulfate ions in the polishing bath since it has a much higher dissociation constant than that of the step. When using other acids, ie acids with dissociation constants that lie between the first and second dissociation stages of sulfuric acid, the concentration of sulfate ions can only be influenced by the concentration of sulfuric acid and the temperature of the polishing bath. As the temperature of the polishing bath increases, the dissociation of sulfuric acid increases. Therefore, the bath temperature should not be too high. This method can be used at room temperature, but requires longer polishing times.

The amount of acid added to a polishing bath containing sulfuric acid and hydrofluoric acid depends to some extent on the respective concentrations of sulfuric acid and hydrofluoric acid. Addition of 1-20g/acid is 40-65% by weight H ₂ SO ₄ and 1.5-12% by weight HF
Generally suitable for polishing baths containing. 45-60
In polishing baths containing % by weight H ₂ SO ₄ and 1.5-6% by weight HF, 1-11 g/acid should be added.

In addition to the advantages already mentioned, the method of the invention also provides:
The consumption of hydrofluoric acid and the loss of silicon tetrafluoride to the exhaust air are significantly reduced compared to known methods which require multiple alternating treatments; this results in a reduction in the amount of silicon tetrafluoride lost to the environment or equipment associated with gas cleaning of the exhaust air. It also has the advantage that its adverse effects are not so great.
The consumption of hydrofluoric acid and sulfuric acid is also significantly reduced compared to known methods, since the required polishing time is short and the most suitable fluoride ion concentration is adjusted. Also, since the desired degree of polishing can be achieved directly after the minimum amount of glass has been removed, the formation of sludge in the polishing bath is correspondingly reduced.

In the polishing bath according to the present invention, a high polishing rate, that is, a relatively short polishing time is achieved,
At the same time, the ability to use the polishing bath will be extended. The concentration of sulfuric acid in the polishing bath is determined by the composition of the glass to be polished, ie by the particular precise condition of the glass containing alkaline earth metal ions, especially calcium. In the polishing bath according to the invention, the sulfuric acid concentration should be between 35% and 65%, and in fact only between 60% and 65% if the glass contains alkaline earth metals. If the sulfuric acid concentration is high, polishing scratches will occur. Such a narrow range of sulfuric acid concentration in the polishing bath for glasses containing alkaline earth metals is a drawback in the case of large scale processing. Also, it cannot be operated in the normal 8 hour exchange method without cleaning or partially renewing in between. During cooling of the polishing bath, precipitation of alkaline earth metal ions may be insufficient, so that the consumption of sulfuric acid for polishing can be relatively high.

The second object of the invention mentioned above, namely, that it can be used during an 8-hour exchange process without special cleaning means or at least partially renewed, and at the same time improves the efficiency and polishing of the polishing bath. The polishing bath, whose quality satisfies all the requirements, can be used in an 8-hour exchange method, during which time the polishing bath according to the invention can be
Add 0.1 to 5 g of sodium chloride and/or potassium chloride to the bath for a certain period of time, and if a decrease in polishing efficiency is observed during the period of use, either all at once or a little at a time after the certain period of use has elapsed. Addition by method is satisfactory. When using sodium chloride and potassium chloride, the total addition amount is generally somewhat less than when adding only one salt, especially about 10%.
less than The reduction in efficiency of the polishing bath may result in either a gradual increase in the total polishing time of the batch in the bath itself or the need to alternate between polishing and cleaning baths several times. Alternatively, if localized polishing scratches occur after using such a polishing bath for some time, such scratches result, for example, in the form of a blue cloud on the surface of the glass article.

If the total polishing time required to achieve the desired degree of polish for the batch is extended by a certain percentage, e.g. 25-50%, or if the polishing scratches, e.g. If, at the first signs of etching, sodium chloride and/or potassium chloride are added to the polishing bath according to the invention, in most cases the polishing scratches in such treated batches disappear again immediately. Also, after a short period of time, the total polishing time required for the desired degree of polishing of the batch returns to normal again. The short time here can be about 10 to 20 minutes. The improved bath according to the invention then allows a flawless polishing quality, economical operation and low acid consumption until the efficiency of the polishing bath decreases once more and salt has to be added again. . However, in order for the polishing bath to be usable without additional cleaning means or without having to renew the bath in the 8-hour exchange process, a single addition of salt approximately halfway through the 8-hour period is usually sufficient. It is enough. If a fresh addition of salt is made at the end of the 8-hour exchange process, then the polishing bath can be regenerated or renewed again, or the polishing bath will once again be at optimum efficiency.

It is noteworthy that the effect achieved by the addition of salts according to the invention is not achieved if only hydrochloric acid is added to the polishing bath.

Besides sulfuric and hydrofluoric acids, the addition of salts to the polishing bath, which includes strong, non-oxidizing acids, reduces calcium ions in solution, as well as other divalent and trivalent ions, such as zinc and The surprising effect was that the polishing bath's ability to retain boron could be enhanced to an extraordinary degree. In the salt-containing bath according to the invention, the number of alternations between polishing bath and cleaning bath is further reduced compared to those of the prior art. Furthermore, it is also possible to polish the glass without damaging it in a so-called single bath treatment without using alternating treatments. It should be noted that in such a treatment, the glassware only needs to be immersed once in the polishing bath for a slightly extended period of time, after which the product can be washed directly after the desired degree of polishing has been achieved.

However, since redissolution of the precipitated salts does not occur when the polishing bath is heated for the first batch, regenerating the polishing bath by salting out at the end of the exchange process or daily is an advantage of the present invention. is not an immediate requirement for polishing baths used in

Other significant advantages, as already mentioned, are that the salt-containing polishing bath according to the invention does not impose narrow limitations as far as the sulfuric acid concentration is concerned, and in particular from the point of view of batch gold polishing time, it is possible to use CaO-containing glasses. This is to enable operation at higher sulfuric acid concentrations, which is preferred. The usable range of sulfuric acid concentration for the _salt -containing method is 35-75 _wt . 60 to 65 as mentioned above in the case of calcium oxide containing glasses.
For sulfuric acid concentrations of 60-75% by weight, such concentrations are possible.

Another advantage of polishing baths containing salt is that the temperature of the polishing bath can be kept significantly lower during the polishing process. It has generally been necessary in the past to maintain the temperature of the polishing bath at about 50-65°C. Therefore, in the present invention, higher sulfuric acid concentrations can be used and the associated advantage is that not only does the risk of "burning" the surface of the glassware disappear, but also it can be carried out at significantly lower temperatures. becomes. It should be noted that the extremely low temperature is a temperature that has conventionally been considered to be common or can be used for polishing glass products with acid. Thereby, the process according to the invention can be carried out satisfactorily in baths at temperatures between 20<0>C and 40<0>C.

A particularly suitable application of the method of the invention is for screen tubes, television tubes, etc. that have been polished with a diamond abrasive wheel and then sandblasted. By means of the method of the invention, a degree of polish previously unachievable for this type of product is achieved with a minimum soaking time, for example about 20 seconds, ie 2.times.10 seconds.

Next, the present invention will be explained with reference to examples.

Example 1 A corundum polished lead crystal glass product with approximately 30% PbO was subjected to a polishing process. The polishing bath has a density of 1.58 g/ ^cm3 at 20°C and a concentration of 50% by weight.
A solution containing H ₂ SO ₄ , 3% by weight of HF and 3 g of oxalic acid (oxalic acid concentration of 0.15% by weight) was used at a temperature of 50°C. The desired degree of polishing was achieved without alternation in a polishing time of 12 minutes.

Example 2 Diamond-polished lead crystal glass with 30% PbO was subjected to polishing treatment. The polishing bath contained 45% by weight H ₂ SO ₄ , 4% by weight HF and
The bath was used at a temperature of 55 DEG C., with a solution containing 7.5 g/ml of uric acid, corresponding to a concentration of 0.35% by weight.
After four 1.5 minute immersions in the polishing bath and transfer to the sulfuric acid wash, the desired degree of polish was achieved in a total polishing time of 10 minutes.

Example 3 As a modification of Example 2, 55% by weight of H ₂ SO ₄ ,
Corresponds to a concentration of 6 wt% HF and 0.7 wt%
A solution containing 11 g/ml of oxalic acid was used. Using this polishing bath, no alternating treatments were required and the desired degree of polishing was achieved after a polishing time of 20 minutes. The consumption of hydrofluoric acid was 30% higher than in Example 2.

Example 4 45% by weight of hand-blown glass containing 24% PbO
of H ₂ SO ₄ , 2.5% by weight of HF and 3 g/tartaric acid corresponding to 0.3% by weight, while maintaining the bath at 50°C. After 20 minutes of polishing time without replacement, the desired degree of polishing was achieved.

Example 5 Extruded glass with 24% by weight PbO was prepared with 60% by weight H ₂ SO ₄ , 5% by weight HF and 1.1% by volume (85% by weight)
Polishing treatment was carried out at a temperature of 50°C using a solution containing phosphoric acid (wt%). The desired degree of polishing was achieved after a polishing time of 15 minutes without alternating treatments.

Example 6 Glassware containing 24% PbO and 4% CaO was treated in a polishing bath containing 70% sulfuric acid, 4.5% hydrofluoric acid and 2.5 g/tartaric acid.
Polished at a temperature of 50℃. The entire polishing process was carried out in 4-5 alternating cycles, depending on the polishing type of the product. Incidentally, such alternating treatment means immersion in a polishing bath followed by immersion in a sulfuric acid cleaning bath. The total polishing time, ie the time during which the glassware was in the polishing bath, was initially 12 minutes and increased to 20 minutes over a 4 hour period of use.

0.3 g of NaC per polishing bath 1 was then added to the polishing bath. After about 15 minutes, a new batch of glassware could be polished and processed within 15 minutes.

Near the end of the 4 hour period of use, and as the total polishing time of the batch increased to 20 minutes, a light blue haze was visible on the glassware, which disappeared immediately after the addition of the salt solution.

Example 7 Corresponding to Example 6, 5% PbO and 5%
Glassware containing CaO was subjected to four alternating treatments and a total polishing time of 15 at 40 °C in a polishing bath containing 75% sulfuric acid, 1.5% hydrofluoric acid and 10 cm ³ of phosphoric acid (75% by weight). Polished and treated in minutes.
Within 4 hours of use, the polishing time was extended to about 20 minutes. 0.1g/NaC and 0.1g/
After adding KC, the polishing time for batches was again 15 minutes. The localized blue discoloration that appeared towards the end of the 4-hour use period was no longer present after salt addition.

Example 8 Corresponding to the above example, glassware containing 28% PbO was exposed to a temperature of 39° C. in a polishing bath containing 65% sulfuric acid, 8% hydrofluoric acid and 6 g/ml oxalic acid. , without requiring alternating processing,
That is, the desired polish was achieved in less than 3.5 minutes with a single bath treatment. After about 4 hours of bath time, blue spots appeared on the glassware and the polishing time slowly increased to 5 minutes. After 15 minutes of addition of 0.5 g/NaC, the polishing time was again reduced to 3.5 minutes to a maximum of 4 minutes.

Claims (1)

[Claims] 1. When polishing a glass product in a polishing bath containing sulfuric acid and hydrofluoric acid and cleaning the polished product with sulfuric acid and/or water, hydrofluoric acid A method for polishing glassware, characterized in that one or more non-oxidizing acids stronger than the polishing bath are added to the polishing bath. 2. The polishing method according to claim 1, wherein an acid stronger than the second dissociation stage of sulfuric acid is added. 3. The polishing method according to claim 1 or 2, wherein one or more of phosphoric acid, monocarboxylic acid, dicarboxylic acid, or hydroxy acid is added. 4 Claim 3 adding oxalic acid, malonic acid, tartaric acid, citric acid and/or phosphoric acid
Polishing method described in section. 5. The polishing method according to claim 1 or 2, wherein 1 to 30 g/acid is added to the polishing bath. 6 1~30g/acid with 40~65% by weight sulfuric acid
The polishing method according to claim 5, wherein the polishing method is added to a polishing bath containing 1.5 to 12% by weight of hydrofluoric acid. 7. A patent for adding an additional 0.1 to 5 g of sodium chloride and/or potassium chloride per polishing bath 1 to the polishing bath during the 8-hour exchange method when the efficiency of the polishing bath decreases and scratches from polishing appear. A polishing method according to any one of claims 1 to 6. 8. The polishing method according to claim 7, wherein sodium chloride and/or potassium chloride are added in portions after about 4 hours of use of the polishing bath. 9. A polishing bath containing 35-75% by weight of sulfuric acid at 20°C.
A polishing method according to claim 7 or 8, which is used for polishing at a temperature of ~40°C. 10 In polishing glass products containing alkaline earth metals, 60 to 75% by weight of the glass products
The polishing method according to claim 7 or 8, wherein polishing is performed in a polishing bath containing sulfuric acid. 11. The polishing method according to claim 10, wherein the temperature during polishing is 20°C to 40°C.